U.S. Pat. No. 5,985,848, U.S. Pat. No. 6,066,722 and U.S. Pat. No. 6,228,741 describe nucleoside analogues that are inhibitors of purine nucleoside phosphorylases (PNPs) and purine phosphoribosyl-transferases (PRTs). The analogues are useful in treating parasitic infections, T-cell malignancies, autoimmune diseases and inflammatory disorders. The analogues are also useful for immunosupression in organ transplantation.
U.S. Pat. No. 6,693,193 describes a process for preparing certain PNP inhibitor compounds. This application recognises the compounds as PNP inhibitors and addresses a need for simpler methods of preparing them. U.S. Ser. No. 10/363,424 discloses further nucleoside analogues that are inhibitors of PNPs and PRTs.
PNPs catalyse the phosphorolytic cleavage of ribo- and deoxyribonucleosides, for example those of guanine and hypoxanthine, to give the corresponding sugar-1-phosphate and guanine, hypoxanthine or other purine bases.
Humans deficient in PNP suffer a specific T-cell immunodeficiency due to an accumulation of dGTP which prevents proliferation of stimulated T lymphocytes. Inhibitors of PNP are, therefore immunosuppressive, and are active against T-cell malignancies and T-cell proliferative disorders.
Nucleoside hydrolases (NHs) catalyse the hydrolysis of nucleosides. These enzymes are not found in mammals but are required for nucleoside salvage in some protozoan parasites. Some protozoan parasites use nucleoside phosphorylases either instead of or in addition to nucleoside hydrolases for this purpose. Inhibitors of nucleoside hydrolases and phosphorylases can be expected to interfere with the metabolism of the parasite and can therefore be usefully employed against protozoan parasites.
5′-Methylthioadenosine phosphorylase (MTAP) and 5′-methylthioadenosine nucleosidase (MTAN) function in the polyamine biosynthesis pathway, in purine salvage in mammals, and in the quorum sensing pathways in bacteria. MTAP catalyses the reversible phosphorolysis of methylthioadenosine (MTA) to adenine and 5-methylthio-α-D-ribose-1-phosphate (MTR-1P). MTAN catalyses the reversible hydrolysis of MTA to adenine and 5-methylthio-α-D-ribose, and of S-adenosyl-L-homocysteine (SAH) to adenine and S-ribosyl-homocysteine (SRH). The adenine formed is subsequently recycled and converted into nucleotides. Essentially, the only source of free adenine in the human cell is a result of the action of these enzymes. The MTR-1P is subsequently converted into methionine by successive enzymatic actions.
MTA is a by-product of the reaction involving the transfer of an aminopropyl group from decarboxylated S-adenosylmethionine to putrescine during the formation of spermidine. The reaction is catalyzed by spermidine synthase. Likewise, spermine synthase catalyses the conversion of spermidine to spermine, with concomitant production of MTA as a by-product. The spermidine synthase is very sensitive to product inhibition by accumulation of MTA. Therefore, inhibition of MTAP or MTAN severely limits the polyamine biosynthesis and the salvage pathway for adenine in the cells.
Although MTAP is abundantly expressed in normal cells and tissues, MTAP deficiency due to a genetic deletion has been reported with many malignancies. The loss of MTAP enzyme function in these cells is known to be due to homozygous deletions on chromosome 9 of the closely linked MTAP and p16/MTS1 tumour suppressor gene. As absence of p16/MTS1 is probably responsible for the tumour, the lack of MTAP activity is a consequence of the genetic deletion and is not causative for the cancer. However, the absence of MTAP alters the purine metabolism in these cells so that they are mainly dependent on the de novo pathway for their supply of purines.
MTA has been shown to induce apoptosis in dividing cancer cells, but to have the opposite, anti-apoptotic effect on dividing normal cells such as hepatocytes (E. Ansorena et al., Hepatology, 2002, 35: 274-280). MTAP inhibitors may therefore be used in the treatment of cancer. Such treatments are described in U.S. Ser. No. 10/395,636 and U.S. Ser. No. 10/524,995.
Compounds where the location of the nitrogen atom in the sugar ring is varied or where two nitrogen atoms form part of the sugar ring, have also been identified as inhibitors of MTAP and MTAN. These compounds are described in U.S. Ser. No. 10/524,995.
The need for new cancer therapies remains ongoing. For some prevalent cancers the treatment options are still limited. Prostate cancer, for example, is the most commonly diagnosed non-skin cancer in the United States. Current treatment options include radical prostatectomy, radiation therapy, hormonal therapy, and watchful waiting. Although the therapies may offer successful treatment of an individual's condition, the pitfalls are quite unfavorable and lead to a decrease in a man's overall quality of life. Surgery may inevitably result in impotence, sterility, and urinary incontinence. Side effects associated with radiation therapy include damage to the bladder and rectum as well as slow-onset impotence. Hormonal therapy will not cure the cancer and eventually most cancers develop a resistant to this type of therapy. The major risk associated with watchful waiting is that it may result in tumour growth, cancer progression and metastasis. It is therefore desirable that alternative treatment options are made available to patients diagnosed with prostate cancer.
MTAP and MTAN inhibitors may also be used in the treatment of diseases such as bacterial infections or protozoal parasitic infections, where it is desirable to inhibit MTAP/MTAN. Such treatments are described in U.S. Ser. No. 10/395,636 and U.S. Ser. No. 10/524,995. However, the search continues for more effective treatments using these inhibitors.
The imino sugar part of the compounds described in the patent specifications referred to above has the nitrogen atom located between C-1 and C-4 so as to form 1,4-dideoxy-1,4-imino-D-ribitol compounds. The location of the nitrogen atom in the ribitol ring may be critical for binding to MTAP and MTAN enzymes. In addition, the location of the link between the sugar moiety and the nucleoside base analogue may be critical for enzyme inhibitory activity. The compounds described above have that link at C-1 of the sugar ring.
The applicants have also developed other MTAP and MTAN inhibitors, where the location of the nitrogen atom in the sugar ring is varied and, additionally, where two nitrogen atoms form part of the sugar ring. Alternative modes of linking the sugar part and the base analogue have also been investigated, resulting in a class of inhibitors where the sugar moiety is linked to the nucleoside base analogue via a methylene bridge. These other inhibitors are described in U.S. Ser. No. 10/395,636.
It has been considered to date that the three dimensional structure of the imino sugar ring of the above compounds is critical for effective binding to MTAP and MTAN, and therefore inhibition of these enzymes. The ring structure constrains the spatial locations that important functional groups, such as the imino nitrogen and various hydroxyl groups, can adopt when interacting with the enzymes. These steric constraints have previously been considered to be necessary for binding of the compounds in the active site of the enzymes. In the absence of such steric constraints, compounds would not be expected to be proficient binders to the enzyme active sites and consequently would not be effective inhibitors of the enzymes.
The view that the imino sugar ring is important for effective enzyme inhibition is reinforced in J. Biol. Chem., 2005, 280, 30320-30328, which describes an investigation of transition state analogue interactions with human and Plasmodium falciparum PNPs. Inhibition activities against these PNPs for various nucleoside analogues are described. The structure of the great majority of the analogues contains an imino sugar ring. However, two compounds are described where that ring is, in effect, opened to give hydroxyethyl and hydroxypropyl substituents on the amino nitrogen.
The applicants surprisingly found that certain compounds analogous to the compounds described above, having an acyclic amine group rather than an imino ring, are effective inhibitors of PNPs. At least one such compound is a surprisingly potent inhibitor of human PNP.
Further investigations were carried out by the applicants into the enzyme inhibitory activity of structurally related compounds, in particular those having an amino group, rather than an hydroxy or alkoxy group, at the 4 position of the heterocyclic part of the compound structure. The applicants have now found that compounds of this type are effective inhibitors of MTAP and/or MTAN.
It is therefore an object of the present invention to provide acyclic amine compounds that are inhibitors of MTAP or MTAN, or to at least provide a useful choice.